Adhesive sheet, adhesive sheet with release film, laminate for image display device, and flexible image display device

Abstract

The purpose of the present invention is to provide: an adhesive sheet having a high refractive index and excellent flexibility; an adhesive sheet with a release film using the adhesive sheet; a laminate for an image display device; and a flexible image display device. This adhesive sheet satisfies the following requirements (1) and (2). Requirement (1): The refractive index of the adhesive sheet is 1.480 or more and less than 1.550. Requirement (2): A shear storage modulus (G '(-20 DEG C)) at-20 DEG C as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 10 kPa or more and 1000 kPa or less.

Description

Technical Field

[0001] The present invention relates to an adhesive sheet, an adhesive sheet with a release film, a laminate for an image display device, and a flexible image display device.

[0002] This application claims priority based on Japanese Patent Application No. 2023-8193 filed with the Japan Patent Office on January 23, 2023, and incorporates its content herein. Background Art

[0003] An image display device has a laminated structure in which a variety of components such as a surface protective film, a cover glass lens, a circularly polarized plate, a touch film sensor, and a light-emitting element are bonded together using a transparent adhesive sheet. Each laminated structure in the image display device can be regarded as a laminated sheet formed by laminating a component and an adhesive sheet.

[0004] In recent years, flexible image display devices using organic light-emitting diodes (OLEDs) and quantum dots (QDs) have been developed and are being widely commercialized. Examples of flexible image display devices include: a bendable type having a curved shape of the image display surface, a foldable type that can be repeatedly bent, a rollable type that can be wound, and a stretchable type that can be stretched.

[0005] For the laminated sheet of a flexible image display device, not only optical properties but also high durability against flexibility, especially against bending, are required.

[0006] However, various problems occur in bendable flexible display devices due to interlayer stress during bending. For the laminated sheet of a flexible display device, for example, when the screen is opened from the folded state, it is required to quickly return to the flat state without leaving the influence caused by the bent state. In addition, during repeated folding operations, the adhesive sheet may peel off, or sometimes the component may crack due to stress applied to the component as the adherend, and ultimately the component may break. Especially during repeated folding operations under severe conditions, i.e., at low temperatures, the laminated sheet is also required to have durability.

[0007] Patent Document 1 discloses a laminated film with an adhesive layer in which there is no concern that the image displayed in the folded portion will be disrupted after repeated bending.

[0008] Patent Document 2 discloses a laminate that does not break or peel even when subjected to a bending test close to the actual use environment. The laminate includes: a double-sided adhesive sheet having a glass transition temperature and a storage modulus within a specified range, and a flexible member for constituting an image display device.

[0009] The laminated sheet of the image display device has the following problems: due to the difference in refractive index between the adhesive sheet and the member, light scattering occurs at the interface between the adhesive sheet and the member, etc. As a result, the light transmittance of the laminated sheet decreases, or spots are generated in the displayed image. This problem is more significant when the surface of the member has irregularities, or in the bent portion of the flexible image display device. Therefore, in order to reduce the refractive index difference between the adhesive sheet and the member, the demand for a high refractive index adhesive sheet is increasing.

[0010] In Patent Document 3, as an adhesive layer for joining various optical members, an adhesive layer containing a base polymer having a glass transition temperature of 5°C or lower and a refractive index of 1.54 or higher is disclosed.

[0011] Prior Art Documents

[0012] Patent Documents

[0013] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-196255

[0014] Patent Document 2: International Publication No. 2018 / 173896

[0015] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2020-132875 Summary of the Invention

[0016] Problems to be Solved by the Invention

[0017] However, in each of the technologies disclosed in Patent Documents 1 and 2, although the durability during bending is considered, the refractive index of the adhesive sheet is not considered.

[0018] Although the adhesive layer disclosed in Patent Document 3 has a high refractive index, since it contains a large amount of high refractive index monomers for increasing the refractive index and the glass transition temperature of the adhesive is high, it is difficult to say that it is soft and flexibility is not considered. Further improvement is required in terms of achieving both flexibility and high refractive index.

[0019] Therefore, an object of the present invention is to provide an adhesive sheet, an adhesive sheet with a release film using the same, a laminate for an image display device, and a flexible image display device, the adhesive sheet having a high refractive index, being soft, and having excellent flexibility.

[0020] Solutions to the Problems

[0021] The present invention includes the following aspects.

[0022] [1] An adhesive sheet formed from an adhesive composition,

[0023] The aforementioned adhesive composition contains a (meth)acrylic copolymer (A),

[0024] The above-mentioned adhesive sheet satisfies the following requirements (1) and (2).

[0025] Requirement (1): The refractive index of the above-mentioned adhesive sheet is 1.480 or more and less than 1.550.

[0026] Requirement (2): The shear storage modulus (G'(-20°C)) at -20°C obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 10 kPa or more and 1000 kPa or less.

[0027] [2] The adhesive sheet according to [1] above, wherein the above-mentioned (meth)acrylic copolymer (A) has a structural unit derived from an aromatic (meth)acrylate (a1) having a refractive index of 1.500 or more.

[0028] [3] The adhesive sheet according to [2] above, wherein the glass transition temperature (Tg) of the homopolymer of the above-mentioned aromatic (meth)acrylate (a1) is 60°C or less.

[0029] [4] The adhesive sheet according to [2] or [3] above, wherein the proportion of the structural unit derived from the above-mentioned aromatic (meth)acrylate (a1) relative to all the structural units of the above-mentioned (meth)acrylic copolymer (A) is 1 to 50% by mass.

[0030] [5] The adhesive sheet according to any one of [1] to [4] above, wherein the glass transition temperature (Tg) defined by the maximum value of Tanδ obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is -20°C or less.

[0031] [6] The adhesive sheet according to any one of [1] to [5] above, wherein the above-mentioned adhesive composition further contains a photoinitiator (B).

[0032] [7] The adhesive sheet according to any one of [1] to [5] above, wherein the above-mentioned adhesive composition further contains a photocurable compound (C).

[0033] [8] The adhesive sheet according to any one of [1] to [5] above, wherein the above-mentioned adhesive composition further contains a photoinitiator (B) and a photocurable compound (C).

[0034] [9] The adhesive sheet according to any one of [1] to [8] above, wherein the ratio (G'(-20°C) / G'(60°C)) of the shear storage modulus G'(-20°C) at -20°C to the shear storage modulus G'(60°C) at 60°C obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 150 or less.

[0035]

[10] The adhesive sheet according to any one of the foregoing [1] to [9], having a maximum strain value (γ max ) when a stress of 2 kPa is applied to the adhesive sheet at 60 °C for 600 seconds, and a residual strain value (γ min ) after removing the stress for 600 seconds, with a recovery rate calculated by the following formula being 60% or more,

[0036] Recovery rate (%) = [(γ max - γ min ) / γ max × 100.

[0037]

[11] The adhesive sheet according to any one of the foregoing [1] to

[10] , having a gel fraction of 30% or more.

[0038]

[12] The adhesive sheet according to any one of the foregoing [1] to

[11] , wherein the (meth)acrylic copolymer (A) has a structural unit derived from an (alkyl)acrylate having 9 to 30 carbon atoms in the alkyl group.

[0039]

[13] The adhesive sheet according to any one of the foregoing [1] to

[12] , wherein the (meth)acrylic copolymer (A) is a block copolymer or a graft copolymer.

[0040]

[14] The adhesive sheet according to any one of the foregoing [1] to

[13] , wherein the (meth)acrylic copolymer (A) has a structural unit derived from a macromonomer (a10).

[0041]

[15] The adhesive sheet according to

[14] , wherein the macromonomer (a10) has a structural unit derived from an (alkyl)acrylate having 9 to 30 carbon atoms in the alkyl group.

[0042]

[16] The adhesive sheet according to

[14] or

[15] , wherein the (meth)acrylic copolymer (A) further has a structural unit derived from an aromatic (meth)acrylate (a1) having a refractive index of 1.500 or more,

[0043] The content ratio (a10 / a1) of the structural unit derived from the macromonomer (a10) in the (meth)acrylic copolymer (A) relative to the structural unit derived from the aromatic (meth)acrylate (a1) is 0.1 to 10 by weight.

[0044]

[17] The adhesive sheet according to any one of the foregoing [1] to

[16] , which is used for bonding a member having unevenness on its surface to a member having an organic light-emitting diode.

[0045]

[18] An adhesive sheet with a release film, which comprises the adhesive sheet described in any one of the foregoing [1] to

[17] , and a release film laminated on at least one surface of the foregoing adhesive sheet.

[0046]

[19] The adhesive sheet described in any one of the foregoing [1] to

[17] is used for a component of a flexible image display device.

[0047]

[20] A laminate for an image display device, which comprises two components of an image display device, and the adhesive sheet described in any one of the foregoing [1] to

[17] . The two components of the image display device are laminated by means of the foregoing adhesive sheet, and at least one of the two components of the image display device has a step with a height difference of 2 μm or more on the contact surface with the foregoing adhesive sheet.

[0048]

[21] A flexible image display device, which comprises the laminate for an image display device described in the foregoing

[20] .

[0049] Effects of the Invention

[0050] According to the present invention, an adhesive sheet, an adhesive sheet with a release film using the same, a laminate for an image display device, and a flexible image display device can be provided. The adhesive sheet has a high refractive index, is soft, and has excellent flexibility. Detailed Description

[0051] The meanings of the terms are as follows.

[0052] “(Meth)acrylate” is a general term for acrylate and methacrylate. The same applies to “(meth)acryloyl”, “(meth)acrylic acid”, “(meth)acrylonitrile”, and “(meth)acrylamide”.

[0053] “(Meth)acrylic copolymer” means a copolymer having a structural unit derived from a (meth)acrylic monomer. The (meth)acrylic copolymer may further have a structural unit derived from a monomer other than the (meth)acrylic monomer (such as styrene, etc.).

[0054] “(Meth)acrylic monomer” means a monomer having a (meth)acryloyl group.

[0055] “Vinyl monomer” means a compound having an ethylenic unsaturated bond (polymerizable carbon-carbon double bond).

[0056] “~” indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value, and also includes the meaning of “preferably greater than the lower limit value” or “preferably less than the upper limit value”.

[0057] In addition, when it is described as "x or more" (x is an arbitrary number), unless otherwise specified, it includes the meaning of "preferably greater than x". When it is described as "y or less" (y is an arbitrary number), unless otherwise specified, it also includes the meaning of "preferably less than y".

[0058] Furthermore, "x and / or y (x, y are arbitrary components)" means at least one of x and y, and refers to the three cases of only x, only y, and x and y.

[0059] [Adhesive sheet]

[0060] One embodiment of the present invention relates to an adhesive sheet.

[0061] The adhesive sheet of the embodiment is formed from an adhesive composition containing a (meth)acrylic copolymer (A).

[0062] The adhesive composition preferably further contains a photoinitiator (B).

[0063] The adhesive composition preferably further contains a photocurable compound (C).

[0064] The adhesive composition may further contain other components other than the (meth)acrylic copolymer (A), the photoinitiator (B), and the photocurable compound (C).

[0065] When the adhesive composition has active energy ray curability, the adhesive sheet of the embodiment is typically formed by curing an adhesive composition containing a (meth)acrylic copolymer (A). In one example, the adhesive sheet is in a state after curing of the active energy ray curable adhesive composition.

[0066] The adhesive sheet of the embodiment satisfies the following requirement (1).

[0067] (1) The refractive index of the adhesive sheet is 1.480 or more and less than 1.550.

[0068] The adhesive sheet that satisfies requirement (1) can reduce the refractive index difference between the components of the image display device and the adhesive sheet, and can suppress diffuse reflection and light spots caused by the refractive index difference.

[0069] From the viewpoint of further reducing the refractive index difference, the refractive index of requirement (1) is preferably 1.482 or more, more preferably 1.485 or more, and further preferably 1.490 or more. From the same viewpoint, the refractive index of requirement (1) is preferably 1.570 or less, more preferably 1.560 or less, further preferably 1.550 or less, and particularly preferably 1.520 or less. The lower limit and the upper limit of the refractive index of requirement (1) can be arbitrarily combined.

[0070] The refractive index of requirement (1) is the value on the surface of the adhesive sheet.

[0071] Regarding the measurement of the refractive index of Requirement (1), an Abbe refractometer was used for measurement under the conditions of a wavelength of 589 nm and 23°C.

[0072] As a method for adjusting the refractive index of Requirement (1), for example, the following can be exemplified: methods for adjusting the composition, molecular weight, type, and addition amount of the photocurable compound of the (meth)acrylic copolymer, and methods for compounding a refractive index adjuster. For example, by making the (meth)acrylic copolymer (A) contain a structural unit derived from an aromatic (meth)acrylate (a1) having a refractive index of 1.500 or more, the refractive index of Requirement (1) can be made 1.480 or more. However, these methods are not limited thereto.

[0073] As the refractive index adjuster, for example, the following can be cited: zirconia particles, niobium oxide particles, tin oxide particles (including phosphorus-doped tin oxide particles, fluorine-doped tin oxide particles, etc.), diamond particles, titanium oxide particles, and other high-refractive-index nanoparticles, monomers having substituted or unsubstituted aromatic groups, resins, polymers, etc. The refractive index adjuster can be appropriately selected one or more kinds not only according to the refractive index but also according to other characteristics required for the adhesive sheet.

[0074] The adhesive sheet of the embodiment also satisfies the following Requirement (2).

[0075] (2) The shear storage modulus (G'(-20°C)) at -20°C obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 10 kPa or more and 1000 kPa or less.

[0076] The adhesive sheet that satisfies Requirement (2) is also soft at low temperatures and has excellent flexibility. For example, even when performing repeated folding operations at a low temperature of -20°C, the members of the adherend as the adhesive sheet are not likely to crack or break.

[0077] From the viewpoint of the shape retention force of the adhesive sheet when not adhered, G'(-20°C) of Requirement (2) is preferably 30 kPa or more, more preferably 50 kPa or more, and further preferably 100 kPa or more. On the other hand, from the viewpoint of the softness of the adhesive sheet in a low-temperature environment, G'(-20°C) of Requirement (2) is preferably 800 kPa or less, more preferably 600 kPa or less, further preferably 400 kPa or less, and particularly preferably 300 kPa or less. The lower limit and the upper limit of G'(-20°C) of Requirement (2) can be arbitrarily combined.

[0078] In order to accurately measure the shear storage modulus G', the following situations need to be avoided: the measurement results vary due to the influence of the measurement fixture caused by the insufficient thickness of the adhesive sheet. Requirement (2) is the value measured on the basis of adjusting the thickness to the range of 0.7 to 1.0 mm. Thus, the shear storage modulus G' can be accurately measured without being affected by the measurement fixture.

[0079] "Adjusting the thickness to the range of 0.7 to 1.0 mm" means that when the thickness of the adhesive sheet as the measurement sample does not meet this range, several sheets are overlapped, etc. to adjust the thickness of the measurement sample to this range. The same applies when the thickness of the measurement sample is specified in other tests.

[0080] The measurement of G'(-20°C) of Requirement (2) is carried out as follows, for example.

[0081] After repeatedly laminating the adhesive sheet to adjust the thickness to 0.7 to 1.0 mm, a circular sample with a diameter of 8 mm is punched out. For the obtained sample, using a rheometer, dynamic viscoelasticity measurement is carried out under the conditions that the measurement fixture is a parallel plate with a diameter of 8 mm, the frequency is 1 Hz, the measurement temperature is -50 to 150°C, and the heating rate is 5°C / minute, and the value of the shear storage modulus (G') at -20°C is read.

[0082] As a method for adjusting G'(-20°C) of Requirement (2) in the adhesive sheet to the aforementioned range, for example, the methods of adjusting the composition, molecular weight of the (meth)acrylic copolymer (A), the type and addition amount of the photocurable compound (C) can be exemplified. However, it is not limited to these methods.

[0083] The adhesive sheet of the embodiment preferably further satisfies the following Requirement (3).

[0084] (3) The glass transition temperature (Tg) defined by the maximum value of Tanδ obtained by dynamic viscoelasticity measurement in the shear mode at a frequency of 1 Hz is -20°C or lower.

[0085] The adhesive sheet that satisfies Requirement (3) has excellent flexibility.

[0086] From the viewpoint of obtaining excellent flexibility, the Tg of Requirement (3) is preferably -25°C or lower, more preferably -28°C or lower, further preferably -30°C or lower, and particularly preferably -35°C or lower. On the other hand, the lower limit is usually -80°C.

[0087] As a method for adjusting the Tg of Requirement (3) to the aforementioned range, for example, not only the methods of adjusting the composition, molecular weight of the (meth)acrylic copolymer (A), the type and addition amount of the photocurable compound (C) can be exemplified, but also the method of adjusting the active energy ray irradiation amount can be exemplified. However, it is not limited to these methods.

[0088] The adhesive sheet of the embodiment preferably further satisfies the following requirement (4).

[0089] (4) The ratio (G'(-20°C) / G'(60°C)) of the shear storage modulus G'(-20°C) at -20°C to the shear storage modulus G'(60°C) at 60°C obtained by dynamic viscoelasticity measurement in the shear mode at a frequency of 1 Hz is 150 or less.

[0090] The adhesive sheet that satisfies requirement (4) has an excellent balance between flexibility and adhesiveness in a low-temperature environment.

[0091] From the viewpoint of improving flexibility in a low-temperature environment, G'(-20°C) / G'(60°C) of requirement (4) is preferably 100 or less, more preferably 80 or less, further preferably 50 or less, particularly preferably 40 or less, and most preferably 30 or less. On the other hand, from the viewpoint of improving adhesiveness, G'(-20°C) / G'(60°C) of requirement (4) is preferably 3 or more, more preferably 5 or more, and further preferably 10 or more. The upper and lower limits of G'(-20°C) / G'(60°C) of requirement (4) can be arbitrarily combined.

[0092] The measurement of G'(-20°C) in requirement (4) is the same as the measurement of G'(-20°C) in requirement (2). Regarding the measurement of G'(60°C) in requirement (4), except for reading the value of the shear storage modulus (G') at 60°C, it is the same as the measurement of G'(-20°C) in requirement (2).

[0093] As a method for adjusting G'(-20°C) / G'(60°C) of requirement (4) to the aforementioned range, for example, not only methods such as adjusting the composition, molecular weight, type, and addition amount of the (meth)acrylic copolymer (A) can be exemplified, but also methods such as adjusting the active energy ray irradiation amount can be exemplified. However, it is not limited to these methods.

[0094] The adhesive sheet of the embodiment preferably further satisfies the following requirement (5).

[0095] (5) The recovery rate calculated by the following formula from the maximum strain value (γ max ) when a stress of 2 kPa is applied to the adhesive sheet at 60°C for 600 seconds and the residual strain value (γ min ) after removing the aforementioned stress for 600 seconds is 60% or more.

[0096] Recovery rate (%) = [(γ max - γ min ) / γ max × 100

[0097] The adhesive sheet satisfying requirement (5) has excellent restorability when bent.

[0098] From the viewpoint of obtaining an adhesive sheet with excellent restorability when bent, the recovery rate of requirement (5) is preferably 65% or more, more preferably 70% or more, still more preferably 75% or more, particularly preferably 80% or more, and most preferably 85% or more. On the other hand, from the viewpoint of enhancing the adhesive strength, the recovery rate of requirement (5) is preferably 99% or less, more preferably 98% or less, still more preferably 97% or less. The lower limit and the upper limit of the recovery rate of requirement (5) can be arbitrarily combined.

[0099] The measurement of the recovery rate of requirement (5) is carried out as follows, for example.

[0100] After repeatedly laminating the adhesive sheet to adjust the thickness to 0.7 - 1.0 mm, a circular sample with a diameter of 8 mm is punched out. For the obtained sample, using a rheometer, the strain (γ max ) after applying a pressure of 2 kPa at 60 °C for 600 seconds and the strain (γ min ) after removing the stress and after 600 seconds are measured. The obtained values are substituted into the following formula to calculate the recovery rate.

[0101] Recovery rate (%) = [(γ max - γ min ) / γ max × 100

[0102] As a method for adjusting the recovery rate of requirement (5) to the aforementioned range, for example, the following can be exemplified: a method of adjusting the composition, molecular weight of the (meth)acrylic acid copolymer (A), the type and addition amount of the photocurable compound, and a method of adjusting the active energy ray irradiation amount. However, it is not limited to these methods.

[0103] The adhesive sheet of the embodiment preferably further satisfies the following requirement (6).

[0104] (6) The gel fraction of the adhesive sheet is 30% or more.

[0105] The adhesive sheet satisfying requirement (6) has excellent cohesive force.

[0106] From the viewpoint of enhancing the cohesive force, the gel fraction of requirement (6) is preferably 35% or more, more preferably 40% or more, still more preferably 45% or more. On the other hand, from the viewpoint of obtaining the adhesive strength, the gel fraction of requirement (6) is preferably 90% or less, more preferably 87% or less, still more preferably 85% or less. The lower limit and the upper limit of the gel fraction of requirement (6) can be arbitrarily combined.

[0107] The measurement of the gel fraction of requirement (6) is carried out as follows, for example.

[0108] Wrap a pre-weighed adhesive sheet with a 150-mesh SUS metal mesh and immerse it in ethyl acetate at 23°C for 24 hours. Thereafter, dry it at 70°C for 4.5 hours, and measure the mass of the adhesive before and after immersion in ethyl acetate, respectively. Take the difference between the two masses as the mass of the undissolved adhesive remaining in the metal mesh (post-immersion mass). Calculate the percentage of the mass of the undissolved adhesive remaining in the metal mesh (post-immersion mass) relative to the mass of the adhesive before immersion in ethyl acetate (pre-immersion mass) as the gel fraction (%) of requirement (6).

[0109] As a method for adjusting the gel fraction of requirement (6) to the aforementioned range, for example, the following methods can be exemplified: methods for adjusting the composition, molecular weight, type, and addition amount of the (meth)acrylic copolymer (A), and methods for adjusting the amount of active energy ray irradiation. However, these methods are not limited thereto.

[0110] The adhesive sheet of the embodiment preferably further satisfies requirement (7) described below.

[0111] (7) When the adhesive sheet is adhered to a polyester film, the adhesive force to the surface of the polyester film is 0.5 N / cm or more under the conditions of 23°C, 50% RH, a peeling angle of 180°, and a peeling speed of 300 mm / min.

[0112] The adhesive sheet that satisfies requirement (7) has excellent adhesiveness, and even when the laminate formed by adhering to an adherend such as a component of an image display device is bent, delamination is not likely to occur, so the durability is excellent.

[0113] From the viewpoint of the adhesiveness of the adhesive sheet, the adhesive force of requirement (7) is preferably 1 N / cm or more, more preferably 2 N / cm or more, and further preferably 3 N / cm or more. There is no particular limitation on the upper limit of the adhesive force of requirement (7), and it can be, for example, 20 N / cm or less.

[0114] The measurement of the adhesive force of requirement (7) is carried out as follows, for example.

[0115] Back-attach a polyester film as a substrate film to one side of the adhesive sheet, cut it into a short strip with a width of 10 mm × a length of 150 mm to make a test piece. Paste the test piece on a polyester film pre-attached to soda-lime glass, and perform autoclave treatment (60°C, gauge pressure 0.2 MPa, 20 minutes) to make an adhesive force measurement sample. For the obtained adhesive force measurement sample, in an environment of 23°C and 50% RH, under the conditions of a peeling angle of 180° and a peeling speed of 300 mm / min, peel the adhesive sheet and the substrate film together from the polyester film adhered to the soda-lime glass, and measure the tensile strength (N / cm) using a load cell as the adhesive force.

[0116] As a method for adjusting the adhesive strength of the adjustment requirement (7), for example, the following methods can be exemplified: a method for adjusting the composition, molecular weight, type of photocurable compound, and addition amount of the (meth)acrylic copolymer (A), and a method for adjusting the amount of active energy ray irradiation. However, the methods are not limited to these.

[0117] The adhesive sheet of the embodiment preferably further satisfies the following requirement (8).

[0118] (8) The total light transmittance is 80% or more.

[0119] The adhesive sheet that satisfies the requirement (8) has excellent transparency and can be used for applications that require transparency, such as image display devices.

[0120] The total light transmittance of the requirement (8) is preferably 85% or more, more preferably 90% or more. The higher the total light transmittance of the requirement (8), the more preferable it is, and the upper limit is not particularly limited.

[0121] The measurement of the total light transmittance of the requirement (8) is carried out according to the standard of JIS-K7361-1 (ISO-13468-1).

[0122] The adhesive sheet of the embodiment preferably further satisfies the following requirement (9).

[0123] (9) The haze is 5% or less.

[0124] The adhesive sheet that satisfies the requirement (9) has excellent transparency and can be used for applications that require transparency, such as image display devices.

[0125] The haze of the requirement (9) is preferably 4% or less, more preferably 2% or less, and further preferably 1% or less. The lower the haze of the requirement (9), the more preferable it is, and the lower limit is not particularly limited.

[0126] The measurement of the haze of the requirement (9) is carried out according to the standard of JIS-K7136 (ISO-14782).

[0127] Regarding the method for adjusting the total light transmittance of the requirement (8) and the haze of the requirement (9), for example, adjusting the composition of the (meth)acrylate copolymer, or using a non-colored photoinitiator, or not containing a colorant is sufficient. In addition, an antioxidant can also be used to suppress coloring accompanied by heating and deterioration over time. However, the methods are not limited to these.

[0128] The adhesive sheet of the embodiment can be a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, each layer of the multi-layer is formed of an adhesive composition containing the (meth)acrylic copolymer (A).

[0129] From the aspect of good processability and easy attainment of excellent unevenness followability, the thickness of the adhesive sheet of the embodiment is preferably 5 μm or more, more preferably 10 μm or more, still more preferably 15 μm or more, and particularly preferably 20 μm or more. From the aspect of easily alleviating stress during bending and making the flexible image display device using the adhesive sheet thinner, the thickness of the adhesive sheet of the embodiment is preferably 100 μm or less, more preferably 80 μm or less, still more preferably 70 μm or less, and particularly preferably 60 μm or less. The lower limit and the upper limit of the thickness of the adhesive sheet can be arbitrarily combined.

[0130] ((Meth)acrylic copolymer (A))

[0131] In the adhesive sheet of the embodiment, one of the adjustment means (1) to (9) is to adjust the composition of the (meth)acrylic copolymer (A).

[0132] Hereinafter, an example of the (meth)acrylic copolymer (A) (hereinafter, also simply referred to as "copolymer (A)") that can be suitably used for the adhesive sheet of the embodiment will be described.

[0133] From the aspect of easily obtaining an adhesive sheet that satisfies requirement (1), the copolymer (A) preferably has a structural unit derived from an aromatic (meth)acrylate (a1) having a refractive index of 1.500 or more (hereinafter, also simply referred to as "aromatic (meth)acrylate (a1)").

[0134] The aromatic (meth)acrylate (a1) is a (meth)acrylate having one or more aromatic groups in one molecule.

[0135] Examples of the aromatic group include phenyl, biphenyl, naphthyl, phenanthryl, anthryl, pyrenyl, etc.

[0136] The aromatic ring may have one or more substituents. The aromatic ring having a substituent means that a substituent is bonded to an atom (such as a carbon atom) constituting the ring skeleton of the aromatic ring. Examples of the substituent include halogens such as F, Cl, Br, I; alkyl groups having 1 to 10 carbon atoms; alkoxy groups having 1 to 10 carbon atoms; acyloxy groups having 2 to 11 carbon atoms, etc.

[0137] Regarding the number of aromatic rings of the aromatic (meth)acrylate (a1), from the viewpoint of increasing the refractive index, it is preferably 2 or more, and from the viewpoint of compatibility, it is preferably 4 or less.

[0138] The aromatic ring can be directly bonded to the (meth)acryloyl group of the aromatic (meth)acrylate (a1), or can be bonded to the (meth)acryloyl group of the aromatic (meth)acrylate (a1) via a linking group. Examples of the linking group include: alkylene, (poly)alkylene glycol, ether, ester, urethane, carbonate, amide, urea, etc.

[0139] From the viewpoint of increasing the refractive index of the adhesive sheet, the refractive index of the aromatic (meth)acrylate (a1) is preferably 1.500 or more, more preferably 1.510 or more, and still more preferably 1.520 or more. In addition, from the viewpoint of ensuring compatibility with other structural units, the refractive index of the aromatic (meth)acrylate (a1) is preferably 1.700 or less, more preferably 1.690 or less, still more preferably 1.600 or less, and particularly preferably 1.550 or less. The lower limit and the upper limit of the refractive index can be arbitrarily combined.

[0140] The refractive index of the aromatic (meth)acrylate (a1) is determined according to the standard of JIS-K7142.

[0141] The refractive index of the aromatic (meth)acrylate (a1) can be the value described in a catalog or the like.

[0142] As the aromatic (meth)acrylate (a1), for example, not only can be exemplified benzyl m-phenoxyacrylate (refractive index: 1.566; polymer Tg: -35 °C), phenethyl o-phenoxyphenoxyacrylate (refractive index: 1.577; polymer Tg: 33 °C), 2-phenylbenzyl acrylate (refractive index: 1.600; polymer Tg: 6 °C), o-phenylphenol acrylate (refractive index: 1.575; polymer Tg: 82 °C), phenoxyethyl acrylate (refractive index: 1.519; polymer Tg: -22 °C), benzyl acrylate (refractive index: 1.519; polymer Tg: 6 °C), phenoxyethyl methacrylate (refractive index: 1.511; polymer Tg: 54 °C), phenyl diethylene glycol acrylate (refractive index: 1.514; polymer Tg: -8 °C), phenyl tetraethylene glycol acrylate (refractive index: 1.507; polymer Tg: -18 °C), nonylphenol ethylene oxide modified acrylate (refractive index: 1.507; polymer Tg: 17 °C), neopentyl glycol - acrylic acid - benzoate (refractive index: 1.501), (1-naphthyl)methyl acrylate (refractive index: 1.595; polymer Tg: 31 °C), but also can be exemplified: 2-acryloyloxyethyl phthalate (refractive index: 1.517), 2-acryloyloxyethyl-2-hydroxyethyl phthalate (refractive index: 1.523), 2-hydroxy-3-phenoxypropyl acrylate (refractive index: 1.526) and other aromatic (meth)acrylates having polar groups; 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone and mixtures thereof and other (meth)acrylates having a benzophenone structure. The aromatic (meth)acrylate (a1) can be used alone or in combination of two or more.

[0143] Among them, from the viewpoint of maintaining the flexibility of the pressure-sensitive adhesive sheet and achieving a high refractive index, the aromatic (meth)acrylate (a1) is preferably m-phenoxybenzyl acrylate, o-phenylphenoxyethyl acrylate, 2-phenylbenzyl acrylate, o-phenylphenol acrylate, phenoxyethyl acrylate, benzyl acrylate, phenyldiethylene glycol acrylate, phenyltetraethylene glycol acrylate, and (1-naphthyl)methyl acrylate; m-phenoxybenzyl acrylate, o-phenylphenoxyethyl acrylate, and phenoxyethyl acrylate are more preferred; and m-phenoxybenzyl acrylate is further preferred.

[0144] From the viewpoint of maintaining the flexibility of the pressure-sensitive adhesive sheet and obtaining bendability, the glass transition temperature (hereinafter also referred to as "polymer Tg") of the homopolymer of the aromatic (meth)acrylate (a1) is preferably 60°C or less, more preferably 50°C or less, 40°C or less, 30°C or less, and 20°C or less, and further preferably 0°C or less, -10°C or less, and -20°C or less, in that order.

[0145] On the other hand, the lower limit is usually -70°C or higher, and from the viewpoint of imparting appropriate cohesive force to the pressure-sensitive adhesive sheet, it is preferably -40°C or higher, more preferably -20°C or higher, further preferably 0°C or higher, and still more preferably 10°C or higher.

[0146] The lower limit and upper limit of the Tg of the polymer may be arbitrarily combined.

[0147] As the polymer Tg of the aromatic (meth)acrylate (a1), a value listed in literature, for example, the value listed in the Polymer Handbook [Polymer HandBook, J. Brandrup, Interscience, 1989] or a monomer catalogue can be used.

[0148] From the viewpoint of high refractive index, the ratio of the structural unit derived from aromatic (meth) acrylate (a1) to the total structural unit of copolymer (A) is preferably 1% by mass or more, more preferably 5% by mass or more, further preferably 8% by mass or more, particularly preferably 10% by mass or more, and particularly preferably 15% by mass. From the viewpoint of maintaining the flexibility of the adhesive sheet and obtaining bendability, the ratio of the structural unit derived from aromatic (meth) acrylate (a1) to the total structural unit of copolymer (A) is preferably 50% by mass or less, more preferably 40% by mass or less, further preferably 35% by mass or less, particularly preferably 30% by mass or less, particularly preferably 25% by mass or less, and most preferably 20% by mass or less. The lower limit and upper limit of the above ratio can be arbitrarily combined.

[0149] From the aspect of obtaining flexibility, the copolymer (A) preferably has, in addition to the structural unit derived from the aromatic (meth)acrylate (a1), a structural unit derived from the (meth)acrylate alkyl ester (a2) having 4 to 30 carbon atoms in the alkyl group.

[0150] In addition, from the viewpoint of obtaining excellent adhesive properties, it is preferable that, in addition to the structural unit derived from the aromatic (meth)acrylate (a1) and the structural unit derived from the (meth)acrylate alkyl ester (a2) having 4 to 30 carbon atoms in the alkyl group, it further has a structural unit derived from any one or more copolymerizable monomers selected from the group consisting of a monomer (a3) containing a carboxyl group, a monomer (a4) containing a hydroxyl group, a nitrogen-containing monomer (a5), a monomer (a6) containing an epoxy group, a vinyl monomer (a7), a (meth)acrylate alkyl ester monomer (a8) having 1 to 3 carbon atoms in the alkyl group, an alicyclic monomer (a9), a macromonomer (a10), and other copolymerizable monomers (a11).

[0151] Among the copolymerizable monomers (a3) to (a11), any one or more selected from the group consisting of a monomer (a3) containing a carboxyl group, a monomer (a4) containing a hydroxyl group, and a nitrogen-containing monomer (a5) are preferred.

[0152] In addition, it is particularly preferable that the monomer (a3) containing a carboxyl group is not contained, and any one or more selected from the group consisting of a monomer (a4) containing a hydroxyl group and a nitrogen-containing monomer (a5) are selected. In the case of the copolymer (A) having a structural unit derived from any one or more selected from the group consisting of a monomer (a4) containing a hydroxyl group and a nitrogen-containing monomer (a5), it is possible to have corrosion resistance characteristics, adhesiveness, and moisture and heat resistance whitening characteristics when the adherend contains corrosive components such as metal.

[0153] Furthermore, among the nitrogen-containing monomers (a5), from the aspect of having a sensitizing effect of the dehydrogenation reaction described later and as a result, being able to efficiently form crosslinks, it is preferable to have a tertiary nitrogen atom.

[0154] The (meth)acrylate alkyl ester (a2) is a linear or branched alkyl (meth)acrylate having 4 to 30 carbon atoms in the alkyl group and is represented by the following formula (1).

[0155] CH2=CH(R 1 )-COO(R 2 ) (1)

[0156] (In the formula, R 1 represents a hydrogen atom or a methyl group, and R 2 represents a linear or branched alkyl group having 4 to 30 carbon atoms)

[0157] Examples of the (meth)acrylic acid alkyl ester represented by the formula (1) include: linear (meth)acrylic acid alkyl esters such as n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, eicosyl (meth)acrylate, heneicosyl (meth)acrylate, behenyl (meth)acrylate; branched (meth)acrylic acid alkyl esters such as sec-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isostearyl (meth)acrylate, isoeicosyl (meth)acrylate, butyloctyl (meth)acrylate, isomyristyl (meth)acrylate, isocetyl (meth)acrylate, hexyl decyl (meth)acrylate, isostearyl (meth)acrylate, octyl decyl (meth)acrylate, octyldodecyl (meth)acrylate, isobehenyl (meth)acrylate. One or more of these can be used, or two or more can be used in combination.

[0158] Among these, from the viewpoints of flexibility and adhesiveness, the number of carbon atoms of the alkyl group is preferably 4 to 20, more preferably 5 or more, further preferably 6 or more, particularly preferably 9 or more, and especially preferably 10 or more. On the other hand, it is preferably 18 or less, more preferably 16 or less, further preferably 15 or less, and particularly preferably 14 or less.

[0159] In addition, from the aspect of further obtaining flexibility, linear (meth)acrylic acid alkyl esters are preferred. Also, from the viewpoint of achieving a balance between adhesiveness and flexibility, the number of carbon atoms of the alkyl group is preferably 4 to 20, more preferably 5 or more, further preferably 6 or more, particularly preferably 9 or more, and especially preferably 10 or more. On the other hand, it is preferably 18 or less, more preferably 16 or less, particularly preferably 15 or less, and especially preferably 14 or less. Examples include: n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate.

[0160] In addition, among these, from the viewpoint of easily causing the dehydrogenation reaction described later upon light irradiation and being able to efficiently form a crosslinking reaction as a result, it is preferable to use a (meth)acrylic acid branched alkyl ester. Among them, it is preferable that the (meth)acrylic acid branched alkyl ester has an alkyl group with 4 to 20 carbon atoms, more preferably 5 to 18 carbon atoms, still more preferably 6 to 16 carbon atoms, and particularly preferably 7 to 14 carbon atoms. For example, sec-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate are preferable.

[0161] Among the (meth)acrylic acid alkyl esters (a2), it is preferable to use a (meth)acrylic acid alkyl ester having a tertiary carbon atom in the alkyl group. By using such a (meth)acrylic acid alkyl ester, the dehydrogenation reaction easily occurs upon light irradiation, and as a result, crosslinking is easily formed efficiently.

[0162] The proportion of the structural unit derived from the (meth)acrylic acid alkyl ester (a2) relative to all the structural units of the copolymer (A) is preferably 5% by mass or more and 95% by mass or less, more preferably 10% by mass or more and 90% by mass or less, still more preferably 15% by mass or more and 85% by mass or less, and particularly preferably 20% by mass or more and 80% by mass or less. If the proportion of the structural unit derived from the (meth)acrylic acid alkyl ester is at least the aforementioned lower limit value, there is a tendency for excellent flexibility and excellent unevenness followability when the adherend has unevenness. If it is at most the aforementioned upper limit value, there is a tendency for easily obtaining the effects of the copolymerizable monomers described later and excellent adhesiveness and cohesion.

[0163] The lower limit and the upper limit of the content of the structural unit derived from the (meth)acrylic acid alkyl ester (a2) can be arbitrarily combined.

[0164] Examples of the monomer (a3) containing a carboxyl group include (meth)acrylic acid, 2-acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxyethyl maleate, 2-(meth)acryloyloxypropyl maleate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxypropyl succinate, crotonic acid, fumaric acid, maleic acid, and itaconic acid. These can be used alone or in combination of two or more.

[0165] As the monomer (a4) containing a hydroxyl group, for example, the following can be cited: 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate and other (meth)acrylic acid hydroxyalkyl esters; caprolactone-modified 2-hydroxyethyl (meth)acrylate and other caprolactone-modified (meth)acrylic acid hydroxy esters; diethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate and other oxyalkylene-modified (meth)acrylic esters; 2-acryloyloxyethyl-2-hydroxyethyl phthalate and other (meth)acrylic esters containing a primary hydroxyl group; 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate and other (meth)acrylic esters containing a secondary hydroxyl group; 2,2-dimethyl-2-hydroxyethyl (meth)acrylate and other (meth)acrylic esters containing a tertiary hydroxyl group; vinyl ethers such as 2-hydroxyethyl vinyl ether, diethylene glycol mono vinyl ether, 4-hydroxybutyl vinyl ether. These can be used alone or in combination of two or more.

[0166] By using the monomer (a4) containing a hydroxyl group, the adhesive strength of the adhesive sheet is improved and the wet heat whitening can be suppressed.

[0167] Among the monomers (a4) containing a hydroxyl group, monomers containing a hydroxyl group having a hydroxyalkyl group with 1 to 10 carbon atoms, further 1 to 6 carbon atoms, especially 2 to 4 carbon atoms are preferred, such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl vinyl ether, diethylene glycol mono vinyl ether, 4-hydroxybutyl vinyl ether, etc. (meth)acrylic esters containing a primary hydroxyl group are particularly preferred, such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate.

[0168] From the viewpoints of imparting adhesive strength and resistance to wet heat whitening, the content of the structural unit derived from the monomer (a4) containing a hydroxyl group in the copolymer (A) is preferably 0.1 to 15% by mass, more preferably 0.5 to 13% by mass, still more preferably 1 to 10% by mass, and particularly preferably 2 to 7% by mass, based on all the structural units of the copolymer (A).

[0169] As the nitrogen-containing monomer (a5), for example, not only monomers containing an amino group, monomers containing an amide group, monomers containing an isocyanate group, etc. can be cited, but also (meth)acrylonitrile, etc. By using the nitrogen-containing monomer (a5), the cohesion of the adhesive sheet is improved and the wet heat whitening can be suppressed. These can be used singly or in combination of two or more. In addition, the nitrogen-containing monomer (a5) has the effect of promoting the dehydrogenation reaction described below.

[0170] As monomers containing an amino group, examples include: (meth)acrylate esters containing a primary amino group such as methyl (meth)acrylate amide, ethyl (meth)acrylate amide; (meth)acrylate esters containing a secondary amino group such as tert-butylaminoethyl (meth)acrylate, tert-butylaminopropyl (meth)acrylate; (meth)acrylate esters containing a tertiary amino group such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, dimethylaminopropyl acrylamide, etc., N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylacetamide, N-vinylcaprolactam, etc.

[0171] As monomers containing an amide group, examples include: (meth)acrylamide; N-alkyl (meth)acrylamides such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-n-butyl (meth)acrylamide, diacetone (meth)acrylamide, N,N'-methylenebis(meth)acrylamide; N,N-dialkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-ethylmethylacrylamide, N,N-diallyl (meth)acrylamide; hydroxyalkyl (meth)acrylamides such as N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide; alkoxyalkyl (meth)acrylamides such as N-methoxymethyl (meth)acrylamide, N-(n-butoxymethyl)(meth)acrylamide, maleimide or its derivatives, etc.

[0172] As monomers containing an isocyanate group, examples include 2-(meth)acryloyloxyethyl isocyanate, their alkylene oxide adducts, etc. The isocyanate group can be protected by a blocking agent such as methyl ethyl ketoxime, 3,5-dimethylpyrazole, 1,2,4-triazole, diethyl malonate.

[0173] Among these, in terms of having a sensitizing effect of the hydrogen abstraction reaction described later and being able to effectively form crosslinks as a result, those having a tertiary nitrogen atom are preferred. For example, (meth)acrylate esters containing a tertiary amino group, N,N-dialkyl (meth)acrylamide, N-vinylpyrrolidone, acryloylmorpholine, etc. are particularly preferred.

[0174] From the viewpoint of imparting cohesiveness and resistance to heat and humidity-induced whitening, the content of the structural units derived from the nitrogen-containing monomer (a5) in the copolymer (A) is preferably 0.1 to 15% by mass, more preferably 0.5 to 13% by mass, still more preferably 1 to 10% by mass, and particularly preferably 2 to 7% by mass, relative to all the structural units of the copolymer (A).

[0175] Examples of the monomer (a6) having an epoxy group include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 4-hydroxybutyl glycidyl ether (meth)acrylate. These can be used alone or in combination of two or more.

[0176] Examples of the vinyl monomer (a7) include compounds having a vinyl group in the molecule. Examples of such compounds include vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl laurate, and vinyl stearate, and aromatic vinyl monomers such as styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes. These can be used alone or in combination of two or more.

[0177] Examples of the (meth)acrylic acid alkyl ester monomer (a8) having 1 to 3 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate. These can be used alone or in combination of two or more.

[0178] From the viewpoint of imparting cohesiveness to the adhesive sheet, the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (a8) in the copolymer (A) is preferably 0.1 to 15% by mass, more preferably 0.5 to 13% by mass, still more preferably 1 to 10% by mass, and particularly preferably 2 to 7% by mass, relative to all the structural units of the copolymer (A).

[0179] Examples of the alicyclic monomer (a9) include cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, and adamantyl (meth)acrylate. These can be used alone or in combination of two or more.

[0180] From the viewpoint of imparting cohesiveness to the adhesive sheet, the content of the structural units derived from the copolymerizable monomer (a9) in the copolymer (A) is preferably 0.1 to 15% by mass, more preferably 0.5 to 13% by mass, still more preferably 1 to 10% by mass, and particularly preferably 2 to 7% by mass, relative to all the structural units of the copolymer (A).

[0181] The macromonomer (a10) is a monomer that can easily extend the carbon number of the side chain when polymerized into a (meth)acrylic polymer (copolymer), for example, it can be extended to 20 or more. By using the macromonomer (a10), the (meth)acrylic polymer (copolymer) can be made into a graft copolymer containing a segment having a structural unit derived from the macromonomer (a10). By making it a graft copolymer, it is preferable in terms of enhancing the cohesion of the copolymer (A) and easily improving the cohesion of the adhesive sheet.

[0182] By selecting the macromonomer (a10) and other monomers and their compounding ratios, the properties of the main chain and side chain of the graft copolymer can be changed.

[0183] As the macromonomer (a10), it is preferable that the backbone component is composed of an acrylic copolymer or a vinyl polymer. As the backbone component of the macromonomer, for example, those exemplified in (meth)acrylic acid alkyl esters (a2) with an alkyl carbon number of 4 to 30, vinyl monomers (a7), (meth)acrylic acid alkyl ester monomers (a8) with an alkyl carbon number of 1 to 3, and alicyclic monomers (a9) can be mentioned.

[0184] Among them, from the aspect of being able to produce an adhesive sheet with excellent cohesion, it is preferable to use (meth)acrylic acid alkyl esters with an alkyl carbon number of 1 to 8, alicyclic monomers, aromatic monomers such as styrene.

[0185] On the other hand, from the aspect of being able to produce an adhesive sheet with moderate cohesion and excellent flexibility, it is preferable to use (meth)acrylic acid alkyl esters with an alkyl carbon number of 9 to 30, preferably 10 to 20.

[0186] These can be used alone or in combination of two or more.

[0187] The macromonomer has a radical polymerizable functional group, or functional groups such as a hydroxyl group, an isocyanate group, an epoxy group, a carboxyl group, an amino group, an amide group, and a thiol group. The macromonomer preferably has a radical polymerizable functional group that can copolymerize with other monomers. The radical polymerizable functional group can contain one or two or more, and particularly preferably one. When the macromonomer has a functional group, the functional group can also contain one or two or more, and particularly preferably one.

[0188] In addition, the radical polymerizable functional group and the functional group can contain any one of them, or can contain both.

[0189] The weight average molecular weight of the macromonomer (a10) is preferably 1000 or more and 40000 or less, more preferably 1500 or more and 20000 or less, and further preferably 2000 or more and 15000 or less.

[0190] The weight-average molecular weight of the macromonomer (a10) is a value converted from standard polystyrene measured by gel permeation chromatography (GPC).

[0191] As the macromonomer, those usually produced by manufacturers (such as macromonomers manufactured by Toagosei Co., Ltd., etc.) can be suitably used.

[0192] With respect to all the structural units of the copolymer (A), the content of the structural units derived from the macromonomer (a10) in the copolymer (A) is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and still more preferably 5% by mass or more and 15% by mass or less. If it is at least the aforementioned lower limit value, the force of phase separation between the segment having the structural units derived from the macromonomer (a10) and the segment formed by other structural units becomes stronger, and the shape retention force of the adhesive sheet when not adhered is more excellent. If it is at most the aforementioned upper limit value, the phase separation structure is likely to collapse during adhesion, and the unevenness followability is more excellent. The lower limit and the upper limit of the aforementioned content can be arbitrarily combined.

[0193] Examples of other copolymerizable monomers (a11) include (meth)acrylates having an alkoxyalkylene glycol skeleton such as methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, butoxypolypropylene glycol (meth)acrylate, methoxypolytetramethylene glycol (meth)acrylate, butoxypolytetramethylene glycol (meth)acrylate, methoxypoly(oxyethylene oxypropylene) glycol (meth)acrylate, butoxypoly(oxyethylene oxypropylene) glycol (meth)acrylate, and (meth)acrylates containing a heterocycle such as tetrahydrofurfuryl (meth)acrylate. These can be used alone or in combination of two or more.

[0194] From the viewpoint of obtaining an adhesive sheet having a high refractive index and excellent flexibility, the content ratio (a10 / a1) of the structural units derived from the macromonomer (a10) to the structural units derived from the aromatic (meth)acrylate (a1) in the (meth)acrylic copolymer (A) is preferably 0.1 to 10 (weight ratio). This content ratio (a10 / a1) is more preferably 0.11 to 5, still more preferably 0.12 to 3, and particularly preferably 0.15 to 2.

[0195] The weight-average molecular weight (Mw) of the copolymer (A) is preferably 50,000 or more and 2,000,000 or less, more preferably 100,000 or more and 1,500,000 or less, and still more preferably 300,000 or more and 1,000,000 or less. When the weight-average molecular weight of the copolymer (A) is at least the aforementioned lower limit value, the durability after laminating the adhesive sheet tends to be good. When the weight-average molecular weight of the copolymer (A) is at most the aforementioned upper limit value, the formability during the production of the adhesive sheet tends to be good. The lower limit and the upper limit of the weight-average molecular weight can be arbitrarily combined.

[0196] The weight-average molecular weight of the copolymer (A) is a value in terms of standard polystyrene measured by gel permeation chromatography (GPC).

[0197] The melt viscosity of the copolymer (A) at 130°C is preferably 20 Pa·s or more and 800 Pa·s or less, more preferably 50 Pa·s or more and 600 Pa·s or less, and still more preferably 100 Pa·s or more and 500 Pa·s or less. When the melt viscosity of the copolymer (A) at 130°C is within the aforementioned range, coating can be carried out by a hot melt method in which the adhesive composition containing the copolymer (A) is directly heated and then coated. The lower limit and the upper limit of the melt viscosity can be arbitrarily combined.

[0198] The melt viscosity can be measured, for example, using a viscoelasticity measuring device Rheosol-G5000 manufactured by UBM Corporation.

[0199] The method for producing the copolymer (A) is not particularly limited, and known polymerization methods can be used.

[0200] Regarding the polymerization method, it can be produced by known polymerization methods such as solution polymerization method, suspension polymerization method, and emulsion polymerization method. For use as an adhesive sheet, the solution polymerization method is preferred.

[0201] With respect to the total amount of the adhesive composition, the content of the copolymer (A) in the adhesive composition forming the adhesive sheet of the embodiment is preferably 50% by mass or more and 99.5% by mass or less, more preferably 75% by mass or more and 99% by mass or less, and still more preferably 90% by mass or more and 98% by mass or less. The lower limit and the upper limit of the content of the copolymer (A) can be arbitrarily combined.

[0202] (Photoinitiator (B))

[0203] The adhesive composition for forming the adhesive sheet preferably contains not only the copolymer (A) but also a photoinitiator (B). By making the adhesive composition contain the photoinitiator (B), curability based on active energy rays can be provided.

[0204] The photoinitiator (B) is a compound that generates active free radical species upon irradiation with light such as ultraviolet light and visible light, more specifically light having a wavelength of 200 nm to 780 nm.

[0205] The photoinitiator (B) can be appropriately selected from known photoinitiators. For example, cleavage-type photoinitiators and hydrogen abstraction-type photoinitiators can be cited.

[0206] Examples of the cleavage-type photoinitiators include: 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-[4-{4-(2-hydroxy-2-methyl-propionyl)benzyl}phenyl]-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylethenyl)phenyl)acetone), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, and derivatives thereof.

[0207] As hydrogen abstraction type photoinitiators, examples include: intermolecular hydrogen abstraction type photoinitiators such as benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, methyl 2-benzoylbenzoate, 4-[(4-methylphenyl)thio]benzophenone, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, etc.; intramolecular hydrogen abstraction type photoinitiators such as methyl benzoylformate, 2-(2-oxo-2-phenyl-acetoxy-ethoxy)ethyl hydroxyphenylacetate, 2-(2-hydroxy-ethoxy)ethyl hydroxyphenylacetate, etc.

[0208] Either a cleavage type photoinitiator or a hydrogen abstraction type photoinitiator can be used, or both can be used in combination. Furthermore, each of the cleavage type photoinitiator and the hydrogen abstraction type photoinitiator can be used alone in one kind, or two or more kinds can be used in combination.

[0209] The photoinitiator (B) preferably contains a hydrogen abstraction type photoinitiator. If the photoinitiator (B) contains a hydrogen abstraction type photoinitiator, a hydrogen abstraction reaction also occurs from the copolymer (A), and not only the photocurable compound (C), but also the copolymer (A) is incorporated into the crosslinked structure, and a crosslinked structure with many crosslinking points can be formed. In addition, among the hydrogen abstraction type photoinitiators, for the intramolecular hydrogen abstraction type photoinitiator, it is preferable in terms of being able to be a starting point for generating free radicals not only for the hydrogen donors in the system but also for itself.

[0210] From the viewpoint of the durability when forming a laminate from the adhesive sheet, the content of the photoinitiator (B) in the adhesive composition for forming the adhesive sheet is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, further preferably 0.5 part by mass or more, and particularly preferably 1 part by mass or more with respect to 100 parts by mass of the copolymer (A). On the other hand, from the viewpoint of ensuring the shape retention and adhesiveness of the adhesive sheet, the content of the photoinitiator (B) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, further preferably 3 parts by mass or less, and particularly preferably 2 parts by mass or less with respect to 100 parts by mass of the copolymer (A). The lower limit and the upper limit of the content of the photoinitiator (B) can be arbitrarily combined.

[0211] (Photocurable compound (C))

[0212] The adhesive composition for forming the adhesive sheet preferably contains not only the copolymer (A), or not only the copolymer (A) and the photoinitiator (B), but also the photocurable compound (C).

[0213] By making the adhesive composition also contain the photocurable compound (C), the curing efficiency based on active energy rays can be improved, and the cohesion after curing with active energy rays can be improved.

[0214] Among them, when the copolymer (A) can undergo a hydrogen abstraction reaction by the action of the photoinitiator (B) or the like, so as to form a sufficient crosslinked structure within and / or between the copolymers, the adhesive composition does not necessarily need to contain the photocurable compound (C).

[0215] The photocurable compound (C) is a compound having one or more radically polymerizable groups. As the radically polymerizable group, a (meth)acryloyl group is preferred.

[0216] Examples of the photocurable compound (C) include: monofunctional (meth)acrylic monomers, polyfunctional (meth)acrylic monomers, and (meth)acrylic oligomers.

[0217] The monofunctional (meth)acrylic monomer has one (meth)acryloyl group.

[0218] Examples of the monofunctional (meth)acrylic monomer include those exemplified as the monomers for forming the copolymer (A).

[0219] Examples of the polyfunctional (meth)acrylic monomer include those having two (meth)acryloyl groups and those having three or more (meth)acryloyl groups.

[0220] As a polyfunctional (meth)acrylic monomer having two (meth)acryloyl groups, examples include: 1,4-butanediol di(meth)acrylate, glycerol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol glycidyl ether di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polypropoxy di(meth)acrylate, bisphenol F polyethoxy di(meth)acrylate, ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, and di(meth)acrylate of an ε-caprolactone adduct of neopentyl glycol hydroxypivalate.

[0221] As a polyfunctional (meth)acrylic monomer having three or more (meth)acryloyl groups, examples include: trimethylolpropane trioxyethyl (meth)acrylate, ε-caprolactone-modified tris(2-hydroxyethyl) isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, (tris(acryloyloxyethyl) isocyanurate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxy tri(meth)acrylate, di-trimethylolpropane tetra(meth)acrylate, etc.

[0222] Among them, from the viewpoint of imparting moderate toughness to the cured product, polyfunctional (meth)acrylic monomers having an alkylene glycol skeleton such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate are more preferred.

[0223] From the viewpoint of imparting moderate softness to the cured product, the molecular weight of the polyfunctional (meth)acrylic monomer is preferably 200 or more, more preferably 300 or more, further preferably 400 or more, and particularly preferably 500 or more. The upper limit of the molecular weight of the polyfunctional (meth)acrylic monomer is usually 3000 or less, preferably 2000 or less.

[0224] (Meth)acrylic oligomers can be either monofunctional or polyfunctional. For example, examples include: polyester (meth)acrylate, epoxy (meth)acrylate, urethane (meth)acrylate, polyether (meth)acrylate, etc.

[0225] Among them, from the viewpoint of imparting appropriate toughness to the cured product, polyfunctional urethane (meth)acrylate is preferred.

[0226] From the aspect of obtaining a cured product with high toughness, in other words, a cured product with appropriate softness when curing the adhesive sheet of the embodiment, the molecular weight of the (meth)acrylic oligomer is preferably 3000 or more, more preferably 5000 or more, further preferably 8000 or more, and particularly preferably 10000 or more. The upper limit of the molecular weight of the (meth)acrylic oligomer is usually 100000 or less, preferably 50000 or less.

[0227] From the viewpoint of being able to impart excellent durability when forming a laminate from the adhesive sheet, the content of the photocurable compound (C) in the adhesive composition for forming the adhesive sheet is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, further preferably 1.0 part by mass or more, and particularly preferably 1.2 part by mass or more with respect to 100 parts by mass of the copolymer (A). On the other hand, from the viewpoint of ensuring the shape retention and adhesiveness of the adhesive sheet, the content of the photocurable compound (C) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, further preferably 3 parts by mass or less, and particularly preferably 2 parts by mass or less with respect to 100 parts by mass of the copolymer (A). The lower limit and upper limit of the content of the photocurable compound (C) can be arbitrarily combined.

[0228] (Other components)

[0229] Various additives such as silane coupling agents, adhesion - imparting resins, plasticizers, antioxidants, light stabilizers, metal deactivators, anti - aging agents, moisture absorbents, polymerization inhibitors, ultraviolet absorbers, rust inhibitors, inorganic particles, sensitizers, pigments, etc. can be added to the adhesive composition for forming the adhesive sheet as needed. Typically, the amounts of these additives are preferably set in such a way that they do not adversely affect the curing of the adhesive sheet or do not adversely affect the physical properties of the adhesive sheet.

[0230] (Method for manufacturing the adhesive sheet)

[0231] The manufacturing method of the adhesive sheet of the embodiment is not particularly limited. For example, the copolymer (A), preferably with a photoinitiator (B), more preferably with a photocurable compound (C), additives, etc. are respectively mixed in a specified amount to prepare an adhesive composition. The adhesive composition is formed into a sheet shape, and crosslinked, that is, a polymerization reaction is carried out to cure it, and processing is appropriately carried out as needed, thereby obtaining the adhesive sheet of the embodiment. Or the adhesive composition is prepared by the foregoing method, coated on the component of the image display device, and the adhesive composition is cured, thereby forming the adhesive sheet of the embodiment.

[0232] As a method for mixing each component, for example, methods using a single-screw extruder, a twin-screw extruder, a planetary mixer, a biaxial mixer, a pressure kneader, etc. can be cited.

[0233] As a method for forming the adhesive composition into a sheet shape, for example, the following can be cited: wet lamination method, dry lamination method, extrusion casting method using a T die head, extrusion lamination method, calendering method, inflation method, injection molding method, liquid injection curing method.

[0234] The adhesive sheet of the embodiment can be formed by dissolving the adhesive composition in an appropriate solvent and coating it using various coating methods.

[0235] The curing of the adhesive composition can be carried out by irradiating active energy rays. For example, the active energy rays are irradiated to the formed body of the adhesive composition, for example, to the one formed by forming the adhesive composition into a sheet, thereby manufacturing the adhesive sheet of the embodiment. In addition to irradiating the active energy rays, heating can also be carried out to further achieve curing.

[0236] The irradiation energy, irradiation time, irradiation method, etc. of the active energy rays are not particularly limited, as long as the photoinitiator can be activated to polymerize the monomer components.

[0237] As the active energy rays to be irradiated, for example, the following can be cited: ionizing radiation rays such as α rays, β rays, γ rays, neutron rays, electron beams, ultraviolet rays, visible light rays. Among them, from the viewpoints of suppressing damage to the components of the image display device and controlling the reaction, ultraviolet rays are preferred.

[0238] Regarding the light source when irradiating the active energy rays, for example, the following can be cited: high-pressure mercury lamp, metal halide lamp, xenon lamp, halogen lamp, LED lamp, fluorescent lamp.

[0239] Regarding the irradiation dose of the active energy rays, from the viewpoint of sufficient curing, the irradiation dose of the active energy rays is preferably 1000 mJ / cm 2 The above, more preferably 2000 mJ / cm 2 The above, further preferably 3000 mJ / cm 2Above, and more preferably 3500 mJ / cm 2 Above. From the viewpoint of curing efficiently, it is preferably 10000 mJ / cm 2 Below, more preferably 7000 mJ / cm 2 Below, further preferably 5000 mJ / cm 2 Below. The lower limit and the upper limit of the irradiation amount of the active energy ray can be arbitrarily combined.

[0240] Since the adhesive sheet of the embodiment described above satisfies the requirements (1) and (2), it has a high refractive index, is soft, and has excellent flexibility. Therefore, the adhesive sheet of the embodiment is suitable for use as a component of a flexible image display device. In addition, it is also suitable for bonding a member having unevenness on its surface to a member having an organic light-emitting diode.

[0241] [Adhesive sheet with a release film]

[0242] Another embodiment of the present invention relates to an adhesive sheet with a release film.

[0243] Preferably, a release film is laminated on at least one surface of the adhesive sheet of the embodiment before bonding, and more preferably, release films are laminated on both surfaces.

[0244] When a release film is provided on both surfaces of the present adhesive sheet, it is preferably formed as a laminate including a lightly peeling film with a relatively low peeling force and a heavily peeling film with a relatively high peeling force. When using the adhesive sheet with a release film having release films provided on both surfaces, first, peel off the release film on one side (lightly peeling film) to expose one surface of the adhesive sheet, bond it to a component of the image display device (designated as the first component), and then bond the image display device component (designated as the second component) to the other surface of the adhesive sheet exposed by peeling off the other release film (heavily peeling film).

[0245] Examples of the release film include: polyester film, polyolefin film, polycarbonate film, polystyrene film, acrylic film, triacetyl cellulose film, and fluororesin film. Among these, polyester film and polyolefin film are preferred, and polyester film is more preferred.

[0246] In addition, from the aspect that it is also easy to peel off from the adhesive sheet after irradiating the active energy ray, the release film preferably has a peeling force of 0.1 N / cm or less measured under the conditions of a peeling angle of 180° and a peeling speed of 300 mm / min.

[0247] From the viewpoints of processability and handleability, the thickness of the release film is preferably 25 μm or more and 500 μm or less, more preferably 38 μm or more and 250 μm or less, and still more preferably 50 μm or more and 200 μm or less. The lower limit and the upper limit of the thickness of the release film can be arbitrarily combined.

[0248] [Laminated body for image display device]

[0249] Another embodiment of the present invention relates to a laminated body for an image display device.

[0250] Two image display device constituent members of the laminated body for an image display device according to the embodiment are laminated by means of the adhesive sheet of the present invention.

[0251] Since the adhesive sheet of the present invention has excellent unevenness followability, it can follow and deform even if the surface of the image display device constituent member has steps, absorb the steps, and bond the two image display device constituent members. In addition, since it has a high refractive index, is soft, and has excellent flexibility, the difference in refractive index between the adhesive sheet and the member is small. As a result, light scattering or the like is not likely to occur at the interface between the adhesive sheet and the member, and a laminated body for an image display device with excellent discernibility can be obtained.

[0252] Examples of the image display device constituent members constituting the laminated body for an image display device include, for example, flat panel image display device constituent members and flexible image display device constituent members. Examples of such image display device constituent members include: flexible displays such as liquid crystal displays and organic electroluminescence (EL) displays, cover lenses (covering films), polarizing plates, polarizing members, retardation films, barrier films, viewing angle compensation films, brightness enhancement films, contrast improvement films, diffusion films, transflective films, electrode films, transparent conductive films, metal mesh films, touch sensor films, light emitting elements, PSA (Pressure Sensitive Adhesive), color filters, flexible printed circuit boards, etc. Any one or two of these can be used in combination. Examples of combinations include: combinations of flexible displays and other image display device constituent members, and combinations of cover lenses and other image display device constituent members.

[0253] The material of the image display device constituent member is not particularly limited. Examples include, for example, resin sheets, thin film glasses, metals, etc. mainly composed of resin components such as urethane resins, norbornene resins, triacetyl cellulose resins, (meth)acrylate resins, epoxy resins, and polyimide resins. Here, the "main component" refers to the component with the largest mass ratio among the components constituting the image display device constituent member, preferably 50% by mass or more, more preferably 55% by mass or more, and still more preferably 60% by mass or more.

[0254] The components of the flexible image display device are bendable components, which refer to the components used in an image display device having a curved surface shape and components that can be repeatedly bent. Particularly preferably, they are components that can be fixed into a bent shape with a curvature radius of 25 mm or more, especially components that can withstand a bending action with a curvature radius of less than 25 mm, and more preferably a curvature radius of less than 3 mm.

[0255] As described above, the components for the image display device may have steps on the surface. For example, the components of the image display device may have various irregularities on the contact surface with the adhesive sheet through wiring, printing, pattern development, surface treatment, embossing, etc.

[0256] The height difference of the steps of the components of the image display device is preferably 2 μm or more, more preferably 3 μm or more, and further preferably 4 μm or more. On the other hand, it is preferably 10 μm or less, more preferably 8 μm or less, further preferably 7 μm or less, and particularly preferably 6 μm or less. The lower limit and the upper limit of the height difference of the steps can be arbitrarily combined.

[0257] The steps of the components of the image display device on the contact surface with the adhesive sheet may be, for example, irregularities provided at intervals of 10 mm or less with a height difference of 2 to 10 μm.

[0258] From the aspect of good processability, the thickness of the laminate for the image display device of the embodiment is preferably 0.02 mm or more, more preferably 0.03 mm or more, and further preferably 0.05 mm or more. From the aspect of making the laminate thinner, the thickness of the laminate for the image display device of the embodiment is preferably 1.0 mm or less, more preferably 0.7 mm or less, and further preferably 0.5 mm or less. The lower limit and the upper limit of the thickness of the laminate for the image display device can be arbitrarily combined.

[0259] The manufacturing method of the laminate for the image display device of the embodiment is not particularly limited.

[0260] For example, an adhesive composition can be coated on the components of the image display device to form an adhesive sheet, or after an adhesive sheet with a release film is pre-formed, it can be adhered to the components of the image display device.

[0261] The method of adhering the adhesive sheet on the surface of the components of the image display device having steps is not particularly limited. For example, known methods such as roller adhesion, pressure adhesion using parallel plates, and diaphragm adhesion can be used. As the adhesion environment, it can be either an atmospheric adhesion method for adhesion under normal pressure or a vacuum adhesion method for adhesion under reduced pressure.

[0262] When laminating the adhesive sheet, heat treatment can be performed. The heating temperature during the heat treatment is preferably 40°C or higher and 100°C or lower, more preferably 50°C or higher and 90°C or lower, and still more preferably 55°C or higher and 85°C or lower.

[0263] When laminating the adhesive sheet, a pressing pressure can be applied to the laminate while performing the heat treatment.

[0264] In addition, when laminating the adhesive sheet, a pressing treatment can be performed using an autoclave while performing the heat treatment.

[0265] [Flexible Image Display Device]

[0266] Another embodiment of the present invention relates to a flexible image display device.

[0267] "Flexible image display device" means an image display device that does not leave bending marks even when repeatedly bent, curved, or wound, and quickly returns to the state before the operation when the bent state, curved state, or wound state is released, and can display an image without strain.

[0268] The flexible image display device of the embodiment includes the laminate for an image display device of the present invention. In the flexible image display device of the embodiment, for example, the laminate for an image display device is disposed on the side opposite to the identification side of the image display panel, that is, the light source side.

[0269] In the flexible image display device of the embodiment, other members may be laminated between the image display panel and the laminate for an image display device of the present invention, and on the side opposite to the image display panel of the laminate for an image display device of the present invention. As the other members, those same as the image display device constituent members exemplified in the description of the laminate for an image display device of the embodiment can be exemplified.

[0270] In the flexible image display device of the embodiment, even if there is a step with a height difference of 2 μm or more on the contact surface between the image display device constituent member and the adhesive sheet, the adhesive sheet follows the step, absorbs the step, and suppresses the generation of bubbles. In addition, even when performing bending, curving, or winding operations in a low-temperature environment, delamination and cracking can be suppressed.

[0271] The present invention is not limited to the foregoing embodiments. The constituent elements in the foregoing embodiments can be appropriately replaced with known constituent elements without departing from the gist of the present invention. In addition, the foregoing modification examples can be appropriately combined.

[0272] Examples

[0273] Hereinafter, the embodiments will be described in more detail by way of examples, but the scope of the present invention is not limited to the content described in the following examples. "Parts" in the examples refer to "parts by mass".

[0274] [Measurement, evaluation]

[0275] The measurement and evaluation in the examples were carried out by the methods shown below.

[0276] (Molecular weight of macromonomer)

[0277] Prepare a 0.2 mass% tetrahydrofuran solution of the macromonomer, and under the following conditions, determine the weight-average molecular weight (Mw) based on standard polystyrene conversion.

[0278] · GPC device: "HLC-8320" manufactured by Tosoh Corporation

[0279] · Column: The following columns manufactured by Tosoh Corporation were used in series. As the guard column, "TSKguardcolumn SuperHZ-L" (4.6 mm ID × 2.0 cm L) manufactured by Tosoh Corporation was used.

[0280] "TSKgel SuperHZM-M" (4.6 mm ID × 15 cm L) × 2 pieces

[0281] "TSKgel SuperHZ2000" (4.6 mm ID × 15 cm L) × 1 piece

[0282] · Injection volume: 10 μL

[0283] · Eluent: Tetrahydrofuran (stabilizer BHT)

[0284] · Flow rate: 0.35 mL / minute

[0285] · Column temperature: 40 °C

[0286] (Molecular weight of (meth)acrylic acid copolymer)

[0287] Prepare a 0.27 mass% tetrahydrofuran solution of the (meth)acrylic acid copolymer, and under the following conditions, determine the weight-average molecular weight (Mw) based on standard polystyrene conversion.

[0288] · GPC device: "HLC-8320" manufactured by Tosoh Corporation

[0289] · Column: Two columns of "TSKgel SuperHZM-H" (6.0 mm ID × 15 cm L) manufactured by Tosoh Corporation were used in series. As the guard column, "TSKguardcolumn SuperHZ-H" (4.6 mm ID × 3.5 cm L) manufactured by Tosoh Corporation was used.

[0290] · Injection volume: 10 μL

[0291] · Eluent: Tetrahydrofuran (stabilizer BHT)

[0292] · Flow rate: 0.5 mL / min

[0293] · Column temperature: 40 °C

[0294] (Non-volatile components, volatile components)

[0295] Place about 1 g of the sample on an aluminum dish, dry it in an oven with a blower at 105 °C for 2 hours, measure the mass before and after drying with an electronic balance, and calculate the non-volatile component concentration using the following formula.

[0296] Non-volatile component concentration (%) = (mass of the dried sample (g) / mass of the sample before drying (g)) × 100

[0297] Based on the calculated non-volatile component concentration, calculate the volatile component concentration using the following formula.

[0298] Volatile component concentration (%) = 100 - non-volatile component concentration (%)

[0299] (Refractive index)

[0300] Remove the release film on one side from the adhesive sheet with a release film prepared in each example, and use an Abbe refractometer (manufactured by ATAGO Co., Ltd., model DR-A1-Plus) to measure the refractive index under the measurement conditions of a wavelength of 589 nm and a temperature of 23 °C.

[0301] (Shear storage modulus G', Tg of the adhesive sheet)

[0302] Remove the release film on one side from the adhesive sheet with a release film prepared in each example, repeatedly laminate it using a hand roller, adjust the thickness to about 0.8 mm, and use the one cut into a circle with a diameter of 8 mm as a sample. Set the obtained sample on a rheometer (manufactured by T.A. Instruments, "DHR-2"), and perform dynamic viscoelasticity measurement under the conditions that the measurement jig is a parallel plate with a diameter of 8 mm, the frequency is 1 Hz, the measurement temperature is -50 to 150 °C, and the heating rate is 5 °C / min. Read the values of the shear storage modulus G' at -20 °C, 25 °C, 60 °C, and 80 °C. Based on the measurement results, calculate the value of G'(-20 °C) / G'(60 °C). In addition, read the temperature at which the maximum point of the loss tangent (tanδ) appears as the glass transition temperature (Tg) of the adhesive sheet.

[0303] (Creep test)

[0304] From the adhesive sheets with release films prepared in each example, the release film on one side was removed, and lamination was repeatedly performed using a hand roller. Samples were prepared by adjusting the thickness to approximately 0.8 mm and punching into circles with a diameter of 8 mm. The obtained samples were placed in a rheometer ("DHR-2" manufactured by T.A. Instruments), and the strain (%) after 600 seconds was measured under the conditions that the measurement jig was a parallel plate with a diameter of 8 mm, the temperature was 60°C, and the pressure was 2 kPa. This value was taken as the creep strain (maximum value).

[0305] (Recovery)

[0306] From the adhesive sheets with release films, the release film on one side was removed, and lamination was repeatedly performed using a hand roller. Samples were prepared by adjusting the thickness to approximately 0.8 mm and punching into circles with a diameter of 8 mm (cylinders with a diameter of 8 mm and a height of approximately 0.8 mm). For the obtained samples, a viscoelasticity measuring device ("DHR-2" manufactured by T.A. Instruments) was used to read the maximum strain value (γ max ) when a stress of 2 kPa was applied at 60°C for 600 seconds and the residual strain value (γ min ) after removing the aforementioned stress for 600 seconds. The recovery rate was calculated according to the following formula.

[0307] Recovery rate (%) = [(γ max - γ min ) / γ max × 100

[0308] (Gel fraction)

[0309] The release films were removed from the adhesive sheets with release films prepared in each example, and these were used as samples.

[0310] The pre-weighed samples were wrapped with a 150-mesh SUS metal mesh and immersed in ethyl acetate at 23°C for 24 hours. Then, they were dried at 70°C for 4.5 hours, and the mass of the insoluble samples remaining in the metal mesh after immersion in ethyl acetate was measured. The percentage of the mass of the insoluble samples remaining in the metal mesh relative to the mass of the samples before immersion in ethyl acetate was calculated as the gel fraction (%).

[0311] (Adhesive force)

[0312] Remove the release film on one-sided of the adhesive sheet with release film made in each example, and laminate a PET film (thickness 50 μm) as the substrate film using a hand roller. Cut it into short strips with a width of 10 mm × a length of 150 mm, and laminate the adhesive surface exposed by peeling the remaining release film onto the PET film (manufactured by Mitsubishi Chemical Corporation, Diafoil S-100, thickness 50 μm) pre-laminated on soda-lime glass using a hand roller. Perform autoclave treatment (60 °C, gauge pressure 0.2 MPa, 20 minutes) on the obtained laminate for final lamination, thereby fabricating a sample for measuring adhesive strength.

[0313] For the obtained sample for measuring adhesive strength, at 23 °C and 50% RH, stretch it at an angle of 180° and at a peeling speed of 300 mm / minute, and simultaneously peel the adhesive sheet and the substrate film from the PET film laminated on soda-lime glass, and measure the tensile strength (N / cm) using a load cell as the adhesive strength.

[0314] (Total light transmittance)

[0315] Remove the release film on one-sided of the adhesive sheet with release film made in each example, and roll-press the exposed adhesive surface onto soda-lime glass (82 mm × 53 mm × thickness 0.55 mm). Then, remove the remaining release film and roll-press it onto soda-lime glass (82 mm × 53 mm × thickness 0.5 mm). Then, perform autoclave treatment (60 °C, gauge pressure 0.2 MPa, 20 minutes) for final lamination, thereby fabricating a sample for measuring optical properties.

[0316] For the sample for measuring optical properties, use a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH5000) to measure the total light transmittance according to ISO-13468-1.

[0317] [Materials used]

[0318] SLMA: A mixture of an alkyl methacrylate with 12 carbon atoms in the alkyl group and an alkyl methacrylate with 13 carbon atoms in the alkyl group, manufactured by Mitsubishi Chemical Corporation, trade name: Acryester SL.

[0319] POB-A: m-Phenoxybenzyl acrylate, manufactured by Kyoeisha Chemical Co., Ltd. (refractive index: 1.566).

[0320] OPPEA: o-Phenylphenoxyethyl acrylate, manufactured by MIWON Co., Ltd., trade name: Miramer M1142 (refractive index: 1.577).

[0321] PO-A: Phenoxyethyl acrylate, manufactured by Kyoeisha Chemical Co., Ltd. (refractive index: 1.519).

[0322] AA: Acrylic acid, manufactured by Mitsubishi Chemical Corporation.

[0323] 4HBA: 4-Hydroxybutyl acrylate, manufactured by Mitsubishi Chemical Corporation.

[0324] nBA: n-Butyl acrylate, manufactured by Mitsubishi Chemical Corporation.

[0325] 2EHA: 2-Ethylhexyl acrylate, manufactured by Mitsubishi Chemical Corporation.

[0326] nOA: n-Octyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.

[0327] MMA: Methyl methacrylate, manufactured by Mitsubishi Chemical Corporation.

[0328] AMBN: 2,2'-Azobis(2-methylbutyronitrile), manufactured by Otsuka Chemical Co., Ltd.

[0329] [Production Example 1]

[0330] 100 parts of SLMA, 0.00075 part of bis[(difluoroboryl)diphenylglyoximato]cobalt(II) as a chain transfer agent, and 58 parts of ethyl acetate were added to a four-necked flask equipped with a stirring device, a thermometer, a condenser, and a nitrogen inlet, and the oxygen was displaced by introducing nitrogen. Then, 0.4 part of AMBN as a polymerization initiator and 2 parts of ethyl acetate were added. Then, the external temperature was raised to 90 °C by a water bath, and the reaction was carried out for 2 hours under reflux. Then, 0.2 part of AMBN and 20 parts of ethyl acetate were added dropwise over 1 hour, and then, it was further maintained for 2 hours under reflux. After that, the reaction solution was cooled to 40 °C to obtain a solution containing a macromonomer (SLMA-MM). By adding ethyl acetate to this solution, the non-volatile component concentration was adjusted to 50 mass%. The weight-average molecular weight of the macromonomer (SLMA-MM) was 9420.

[0331] [Production Example 2]

[0332] 900 parts of deionized water, 60 parts of sodium 2-ethylsulfonate methacrylate, 10 parts of potassium methacrylate, and 12 parts of MMA were added to a polymerization apparatus equipped with a stirrer, a condenser, and a thermometer and stirred, and the inside of the polymerization apparatus was purged with nitrogen and heated to 50 °C. 0.08 part of 2,2'-azobis(2-methylpropionamidine) dihydrochloride as a polymerization initiator was added thereto, and the temperature was further raised to 60 °C. After the temperature rise, MMA was continuously added dropwise at a rate of 0.24 part / minute for 75 minutes using a dropping pump. After the reaction solution was maintained at 60 °C for 6 hours, it was cooled to room temperature to obtain Dispersant 1 having a solid content of 10 mass% as a transparent aqueous solution.

[0333] Into a polymerization apparatus equipped with a stirrer, a cooling pipe, and a thermometer, 145 parts of deionized water, 0.1 part of sodium sulfate, and 0.25 part of dispersant 1 (10% by mass of solid content) were added and stirred to prepare a uniform aqueous solution. Next, 100 parts of MMA, 0.0035 part of bis[(difluoroboryl)diphenylglyoxime]cobalt(II) as a chain transfer agent, and 0.35 part of Perocta O (manufactured by NOF Corporation) as a polymerization initiator were added to prepare an aqueous suspension. Next, the inside of the polymerization apparatus was purged with nitrogen, heated to 80°C, and reacted for 1 hour. Further, to increase the polymerization rate, the temperature was raised to 90°C and maintained for 1 hour. Then, the reaction solution was cooled to 40°C to obtain an aqueous suspension containing a macromonomer. The aqueous suspension was filtered, the filtrate was washed with deionized water, dehydrated, and dried at 40°C for 16 hours to obtain a macromonomer (MMA-MM) having MMA as a structural unit.

[0334] The weight-average molecular weight of the macromonomer (MMA-MM) was 5,800.

[0335] [Example 1]

[0336] [Manufacture of (meth)acrylic copolymer]

[0337] Into a four-necked flask equipped with a stirring device, a thermometer, a cooling pipe, and a nitrogen inlet, 25 parts of ethyl acetate as an added solvent, 2 parts of isopropyl alcohol (IPA), and 15 parts of a macromonomer (SLMA-MM) solution (concentration: 50% by mass) were added. Under nitrogen gas flow, the external temperature was raised to 85°C by a water bath. After the reflux state became stable, a mixture containing 20 parts of ethyl acetate, 10 parts of POB-A, 75 parts of nBA, and 0.13 part of Nyper BK40 MT (manufactured by NOF Corporation) was added dropwise over 4 hours. After the addition was completed and held for 1 hour, a mixture containing 0.3 part of Perocta O (manufactured by NOF Corporation) and 15 parts of ethyl acetate was added over 1 hour. Thereafter, after holding for 2 hours, 0.5 part of "Irganox 1010" (trade name, manufactured by BASF Corporation) as an antioxidant and 23 parts of ethyl acetate were added, and the mixture was cooled to room temperature to obtain a (meth)acrylic copolymer (SLMA-MM / POB-A / nBA (mass ratio) = 15 / 10 / 75, weight-average molecular weight: 510,000).

[0338] [Production of adhesive sheet]

[0339] 100 parts by weight of a (meth)acrylic copolymer (solid content), 1.5 parts by weight of a (meth)acrylic oligomer as a photocurable compound (manufactured by Mitsubishi Chemical Corporation, UV-3700B), 1.5 parts by weight of a photoinitiator (manufactured by IGM, Esacure TZT), and 154.5 parts by weight of ethyl acetate were mixed to prepare an adhesive composition containing a solvent. The adhesive composition was spread into a sheet on a release film with a thickness of 100 μm (PET film with silicone release treatment, manufactured by Mitsubishi Chemical Corporation) so that the dried thickness became 50 μm.

[0340] Next, the sheet-like adhesive composition together with the release film was placed in a dryer heated to 90°C and held for 10 minutes to volatilize the solvent contained in the adhesive composition. Further, a release film with a thickness of 75 μm (PET film with silicone release treatment, manufactured by Mitsubishi Chemical Corporation) was laminated on the sheet-like adhesive composition after the solvent was dried, and using a high-pressure mercury lamp, the adhesive composition was irradiated with active energy rays through the release film so that the cumulative light amount at a wavelength of 365 nm became 4000 mJ / cm 2 . As a result, an adhesive sheet with release films laminated on both the front and back sides of a 50-μm-thick adhesive sheet was obtained.

[0341] [Examples 2 to 11, Comparative Examples 1 and 2]

[0342] An adhesive sheet with release films was produced in the same manner as in Example 1, except that the copolymer composition of the (meth)acrylic copolymer was changed as shown in Table 1.

[0343] The adhesive sheets of each example were measured and evaluated, and the results are shown in Table 1.

[0344] [Table 1]

[0345]

[0346] As shown in Table 1, the refractive indices of the adhesive sheets of Examples 1 to 11 were as high as 1.480 or more. In addition, it was found that G'(-20°C) was 10 kPa or more and 1000 kPa or less, and the flexibility at low temperatures was excellent. Furthermore, the adhesive strength was also good. In particular, it was found that the recovery rates of the adhesive sheets of Examples 3 to 8 were as high as 90% or more, and the recovery properties during bending were excellent.

[0347] On the other hand, compared with the adhesive sheets of the examples, the refractive index of the adhesive sheet of Comparative Example 1 was low.

[0348] The shear storage modulus (G'(-20°C)) of the adhesive sheet of Comparative Example 2 at -20°C exceeded 1000 kPa, and it lacked flexibility at low temperatures.

[0349] Industrial Applicability

[0350] According to the present invention, an adhesive sheet, an adhesive sheet with a release film using the same, a laminate for an image display device, and a flexible image display device can be provided. The adhesive sheet has a high refractive index, is soft, and has excellent flexibility.

Claims

1. An adhesive sheet formed from an adhesive composition, The adhesive composition contains a (meth)acrylic copolymer (A), The adhesive sheet satisfies the following requirements (1) and (2), Requirement (1): The refractive index of the adhesive sheet is greater than or equal to 1.480 and less than 1.550; Requirement (2): The shear storage modulus at -20°C (G'(-20°C)) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 10 kPa or more and 1000 kPa or less.

2. The adhesive sheet according to claim 1, wherein The (meth)acrylic copolymer (A) has a structural unit derived from an aromatic (meth)acrylate (a1) having a refractive index of 1.500 or more.

3. The adhesive sheet according to claim 2, wherein The glass transition temperature (Tg) of the homopolymer of the aromatic (meth)acrylate (a1) is 60° C. or less.

4. The adhesive sheet according to claim 2, wherein The ratio of the structural unit derived from the aromatic (meth)acrylate (a1) to the total structural units of the (meth)acrylic copolymer (A) is 1 to 50% by mass. The pressure-sensitive adhesive sheet according to claim 1 , wherein the glass transition temperature (Tg) defined by the maximum value of Tan δ obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is −20° C. or less.

6. The adhesive sheet according to claim 1, wherein The adhesive composition further contains a photoinitiator (B).

7. The adhesive sheet according to claim 1, wherein The adhesive composition further contains a photocurable compound (C).

8. The adhesive sheet according to claim 1, wherein The adhesive composition further contains a photoinitiator (B) and a photocurable compound (C). 9 . The pressure-sensitive adhesive sheet according to claim 1 , wherein the ratio of the shear storage modulus G′(-20° C.) at −20° C. to the shear storage modulus G′(60° C.) at 60° C. (G′(-20° C.) / G′(60° C.)) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 150 or less.

10. The adhesive sheet according to claim 1, wherein the maximum strain value (γ max ) and the residual strain value (γ min ) The recovery rate calculated by the following formula is 60% or more, Recovery rate (%) = [(γ max -γ min ) / γ max ]×100.

11. The pressure-sensitive adhesive sheet according to claim 1, which has a gel fraction of 30% or more.

12. The adhesive sheet according to claim 1, wherein The (meth)acrylic copolymer (A) has a structural unit derived from an alkyl (meth)acrylate having an alkyl group with 9 to 30 carbon atoms.

13. The adhesive sheet according to claim 1, wherein The (meth)acrylic copolymer (A) is a block copolymer or a graft copolymer.

14. The adhesive sheet according to claim 1, wherein The (meth)acrylic copolymer (A) has a structural unit derived from a macromonomer (a10).

15. The adhesive sheet according to claim 14, wherein The macromonomer (a10) has a structural unit derived from an alkyl (meth)acrylate having an alkyl group with 9 to 30 carbon atoms.

16. The adhesive sheet according to claim 14, wherein The (meth)acrylic copolymer (A) further has a structural unit derived from an aromatic (meth)acrylate (a1) having a refractive index of 1.500 or more. The content ratio (a10 / a1) of the structural unit derived from the macromonomer (a10) in the (meth)acrylic copolymer (A) relative to the structural unit derived from the aromatic (meth)acrylate (a1) is 0.1 to 10 by weight ratio. 17 . The adhesive sheet according to claim 1 , which is used to bond a member having an uneven surface to a member having an organic light emitting diode. 18 . A pressure-sensitive adhesive sheet with a release film, comprising the pressure-sensitive adhesive sheet according to claim 1 , and a release film laminated on at least one surface of the pressure-sensitive adhesive sheet.

19. The pressure-sensitive adhesive sheet according to any one of claims 1 to 17, which is used for a component member of a flexible image display device.

20. A laminate for an image display device, comprising two image display device constituent members and the pressure-sensitive adhesive sheet according to any one of claims 1 to 17, The two image display device constituent members are stacked via the adhesive sheet. At least one of the two image display device constituent members has a step having a height difference of 2 μm or more on a contact surface with the pressure-sensitive adhesive sheet. 21 . A flexible image display device comprising the laminate for an image display device according to claim 20 .

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